# Algebraic simplification problem after a u-substitution derivation

The attached file contains a function that needs to have the first order derivative taken. I took the derivative, but I am making a mistake in the algebra simplification of the result. Would you please take a look.

I am working on a dynamic programming problem, and one part of it requires that I take the derivative of the function.

Below is the work that I did.

My study partner worked it out like this:

I think there is a sign mistake in my partner's work. He thinks there is a sign mistake in mine.

Would you work the problem and let me see where the mistake is?

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#### Solution Preview

There's a mistake in your partner's work:

From ... f '(x) = 4x + [ (2/5) * ...

#### Solution Summary

The algebraic simplification problem for after u-substitution derivations are determined.

$2.19